China's Space Program News Thread
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Engineer
Major
It's not all about insulating from lunar night. During the day the rover needs to radiate heat away, so the internal has to be exposed.
Engineer
Major
Monochrome or color? Visible spectrum or infrared region? It makes little sense to compare resolution if the cameras are not seeing the same thing.
coolieno99
Junior Member
Meter-level resolution for a satellite-based SAR is very impressive.
schlieffen
New Member
GF-3 is a SAR satellite. It does not have optical instruments.
Usually one doesn't want to put optical and microwave instruments on the same spacecraft, for a number of reasons.
The only exception I can recall is the monstrous Soviet Almaz-T automatic military space station.
schlieffen
New Member
Spatial resolution is an important specification of a remote sensing spacecraft, but it’s far from the only important one. It’s not a ‘I have a bigger xx’ kinda stupid competition.
The operational requirement of the user usually consists of several conflicting requirements, such as spatial resolution, time resolution (revisit time), swath width, pointing coverage, pointing accuracy, etc. Like all engineering practices it’s all about compromise and prioritize.
To start with, GF-2 is a 100% CIVILIAN satellite. Like in many other countries civilian remote sensing satellites does not represent the best of its technologies. Also civilian users usually don’t put spatial resolution on the top of priorities. While GaoFeng means ‘high resolution’ indeed, that does not necessarily imply spatial resolution.
For example, GF-2 does not represent an improvement over GF-1. Had it not been the CBERS-3 launch failure, it should have been launched last year, only one year after GF-1. They’re the same generation of spacecraft, with different priorities: GF-1 emphasis time resolution, enabled by the astonishing 800km swath width of its four 16m-resolution cameras, while GF-2 put more emphasis on spatial resolution.
That said, GF-2 also has an unusually large swath width (45km) for a satellite of its caliber, about twice as large as similar satellites (Worldview, Pléiades, etc). This is enabled by the use of TWO cameras, each with an aperture of 50cm and focal length of 7m. Obviously this is a compromise between spatial resolution and coverage. If they sacrifice swath width, on the weight/space budget of two cameras it shouldn’t be very difficult to install one camera with slightly larger aperture or longer focal length (or both), and I’d say a ~0.5m resolution isn’t very hard to achieve.
Probably the primary users consider 0.8 m good enough for now, and prefer twice the coverage. That’s perfectly understandable. Remember, even in the US, satellite images sharper than two feet are off-limit to non-govemental users until less around two years ago. 0.8m is really good for civilian use, that’s about the same as the best quality images on Google Earth. Also for civilian users, multi-spectral resolution is often more important than panchromatic.
The operational requirement of the user usually consists of several conflicting requirements, such as spatial resolution, time resolution (revisit time), swath width, pointing coverage, pointing accuracy, etc. Like all engineering practices it’s all about compromise and prioritize.
To start with, GF-2 is a 100% CIVILIAN satellite. Like in many other countries civilian remote sensing satellites does not represent the best of its technologies. Also civilian users usually don’t put spatial resolution on the top of priorities. While GaoFeng means ‘high resolution’ indeed, that does not necessarily imply spatial resolution.
For example, GF-2 does not represent an improvement over GF-1. Had it not been the CBERS-3 launch failure, it should have been launched last year, only one year after GF-1. They’re the same generation of spacecraft, with different priorities: GF-1 emphasis time resolution, enabled by the astonishing 800km swath width of its four 16m-resolution cameras, while GF-2 put more emphasis on spatial resolution.
That said, GF-2 also has an unusually large swath width (45km) for a satellite of its caliber, about twice as large as similar satellites (Worldview, Pléiades, etc). This is enabled by the use of TWO cameras, each with an aperture of 50cm and focal length of 7m. Obviously this is a compromise between spatial resolution and coverage. If they sacrifice swath width, on the weight/space budget of two cameras it shouldn’t be very difficult to install one camera with slightly larger aperture or longer focal length (or both), and I’d say a ~0.5m resolution isn’t very hard to achieve.
Probably the primary users consider 0.8 m good enough for now, and prefer twice the coverage. That’s perfectly understandable. Remember, even in the US, satellite images sharper than two feet are off-limit to non-govemental users until less around two years ago. 0.8m is really good for civilian use, that’s about the same as the best quality images on Google Earth. Also for civilian users, multi-spectral resolution is often more important than panchromatic.
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schlieffen
New Member
Chinese military is extremely tight-lipped about their reconnaissance satellites, like their American counterparts. Technically the military satellites don’t even exist: YG series are always used for ‘remote sensing, disaster mitigation and scientific purposes’. So we can only speculate their performance. My gut felling is that it should be at least as good as the level of technology demonstrated by the GF series, with around 3-4 years lead in time.
BTW, the extremely high resolution of the Crystal series of optical reconnaissance satellites (KH-11/12) is required because of very specific requirements of the US military, namely strategic reconnaissance of the Soviet/Chinese territory. The highest priority targets are strategic weapon production/deployment. The US invested a tremendous amount of resource into this, with around half of the NRO ELINT constellation wholly dedicated to intercepting the Soviet/Chinese ICBM telemetry.
Being strategic spying, it also means you don't really need to know it real-time, just an update once a few months. The orbit design of later KH-11/12s are such that the optimal observation opportunity occurs only twice a year for mid-latitude targets (lowest orbit height and direct over-the-top). For the rest of the year, the satellite pass over much higher and maximum resolution is actually not achievable. While this is a small sacrifice, the new orbit with its much higher apogee significantly reduced the orbital decay rate, and increased the service life of the satellite from the earlier 2-3 years to 10+ years.
Thanks to the mutual inspection liabilities of arm control treaties, the US later gained access to much of the Soviet/Russian nuclear arm establishments, but they’re never fully assured that the Russians are not hiding anything behind the veil (same apply to the Russians). Not to mention they never have that kind of access to Chinese installations (and later the rogue states). As a results, investment on extremely-high resolution spy sats must continue, as there are no ‘good enough’ for probing the other side’s WMD.
This requirement does not exist for any other countries, with the possible exception of Russia, so I don’ think other countries including China are really going to pursuer sub-centimeter resolution, until the advancement of technology make it easy and cheap.
BTW, the extremely high resolution of the Crystal series of optical reconnaissance satellites (KH-11/12) is required because of very specific requirements of the US military, namely strategic reconnaissance of the Soviet/Chinese territory. The highest priority targets are strategic weapon production/deployment. The US invested a tremendous amount of resource into this, with around half of the NRO ELINT constellation wholly dedicated to intercepting the Soviet/Chinese ICBM telemetry.
Being strategic spying, it also means you don't really need to know it real-time, just an update once a few months. The orbit design of later KH-11/12s are such that the optimal observation opportunity occurs only twice a year for mid-latitude targets (lowest orbit height and direct over-the-top). For the rest of the year, the satellite pass over much higher and maximum resolution is actually not achievable. While this is a small sacrifice, the new orbit with its much higher apogee significantly reduced the orbital decay rate, and increased the service life of the satellite from the earlier 2-3 years to 10+ years.
Thanks to the mutual inspection liabilities of arm control treaties, the US later gained access to much of the Soviet/Russian nuclear arm establishments, but they’re never fully assured that the Russians are not hiding anything behind the veil (same apply to the Russians). Not to mention they never have that kind of access to Chinese installations (and later the rogue states). As a results, investment on extremely-high resolution spy sats must continue, as there are no ‘good enough’ for probing the other side’s WMD.
This requirement does not exist for any other countries, with the possible exception of Russia, so I don’ think other countries including China are really going to pursuer sub-centimeter resolution, until the advancement of technology make it easy and cheap.
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broadsword
Brigadier
TerraN_EmpirE
Tyrant King
joshuatree
Captain
Hainan Wenchang Space Center
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